The present invention relates to a device for filtering liquids, comprising an annular disc having two opposite annular side walls spaced from each other, at least one of the side walls being perforated, a plurality of separate sections of a filter medium, each of which covers a part of the perforated side wall, and frames onto which the respective sections of filter medium are applied.
The present invention also relates to a filter unit for use in such a device.
U.S. Pat. No. 3,363,770 discloses a filtering device of this kind, in which each section of filter medium is applied on a separate portion of the perforated wall of the same size as the section of filter medium. Each set of the section of filter medium and its associated perforated wall portion is slided into a frame-like holder on the disc. When exchanging a defective section of filter medium it is initially pushed out from the frame-like holder together with the associated perforated wall portion. Then, the defective section can be removed from its perforated wall portion. However, it is rather complicated to mount a new section of filter medium, since this usually comprises a flexible material, such as cloth, which can easily be dislodged from the intended position on its perforated wall portion, when the set of the new section of filter medium and its perforated wall portion is slided into the frame-like holder.
In current conventional disc filter devices, specifically for treating pulp suspensions, the side walls of the disc comprise several separate perforated wall portions arranged in series around the centre of the disc. The wall portions of one of the side walls of the disc are situated in front of the wall portions of the other side wall of the disc, so that pairs of opposite wall portions are formed. Each such pair of wall portions is enclosed by a filter bag formed from the filter medium, the pair of wall portions and the filter bag forming a sheet-shaped filter segment which is removable from the disc.
If the filter bag of any filter segment becomes defective it has to be exchanged for a new filter bag. To enable such an exchange of filter bags the entire filter segment has to be dismounted manually from the disc. Since the filter segments of these conventional devices may have a weight of up to about 30 kg/unit, it is a troublesome and heavy work to dismount and mount such filter segments. In addition, the work for exchanging defective filter bags is relatively time consuming, and consequently, the downtime costs in this connection are relatively high.
The object of the present invention is to provide a filtering device, which facilitates and permits a rapid exchange of defective parts of the filter medium. This object is obtained by means of a device of the kind stated initially, which is characterized in that the separate sections of filter medium are attached to the frames, such that each section and its frame form a filter unit separate from the perforated side wall, each filter unit being releasably connected to the disc. This has the advantage that a filter unit with a defective filter medium can be readily and quickly exchanged for a new filter unit. In comparison with the above described filter segments of current conventional devices the filter units according to the invention can be made subtantially lighter. In addition to this, the operation for exchanging the filter units according to the invention will be substantially less time consuming, as compared with the operation for exchanging conventional filter bags.
Preferably, the disc is provided with holding means, which engages with the filter units to keep them in intended positions relative to the disc, the holding means having separate parts engaging with radially outer ends of the filter units and being releasably attached to the disc. The holding means is arranged such that the filter units are displaceable substantially radially out from the disc, when said separate parts of the holding means are released from the disc.
In a device according to the invention, in which both side walls are perforated, the filter units are suitably orientated along the side walls, such that pairs of opposite filter units are formed. The radially outer ends of each pair of filter units are advantageously kept in place by one of said releasable parts of the holding means.
The invention also relates to a filter unit for use in the new invented device, the filter unit including a frame defining a filtering area, and a filter medium, which is attached to the frame and covers said filtering area.